Treatments for cardiovascular conditions caused by restricted or blocked blood vessels increasingly involve trauma minimizing non-invasive surgical techniques. For example, in an angioplasty procedure, an elongated and relatively thin catheter can treat a blood vessel restriction, commonly referred to as a stenosis or occlusion, by advancing through the vessel to a location proximate the restriction. A balloon disposed distally on the end of the catheter radially expands against the restriction to open the vessel for increased bloodflow. However, because many angioplasty catheters comprise "over the wire" designs, in order for the catheter to reach the stenosed location, a guide wire typically must first define the vascular path.
Conventional angioplasty guide wires typically include a proximal shaft comprising a solid wire or a solid wall tube with an outer diameter equal to the nominal size of the guide wire. The shaft primarily functions to guide and support a catheter, and to smoothly transmit rotation from the proximal end to an intermediate section. The intermediate section extends axially from the proximal shaft and generally comprises a tapered core wire surrounded by a coiled spring and typically has more flexibility than the proximal shaft. Like the proximal shaft, the intermediate section must assist in guiding the catheter and smoothly transmitting rotation. However, some degree of flexibility in the intermediate section is desirable to conform the catheter to the curvature of the aortic arch and the coronary arteries. Extending from the intermediate section at a distal joint is a flexible distal tip that accepts a pre-formed curved shape resembling a "J". The curved tip tends to steer the guide wire in the direction of the hook.
To reach a blood vessel restriction, conventional guide wires typically traverse tortuous paths having relatively sharp turns and passage constrictions. A common technique to aid in steering the guide wire, especially where the path branches into a plurality of passages, involves rotating the shaft to redirect the pre-formed "J" towards a particular branch, then advancing the wire once the correct orientation is achieved. Unfortunately, as the wire advances into blood vessels of reduced diameter, the friction generated between the guide wire and the inner walls of the vessel tends to inhibit rotation from the proximal shaft, through the intermediate section to the distal tip. Consequently, overly flexible intermediate sections are susceptible to substantial twisting and doubling over, thereby failing to transmit the desired rotation to the distal end of the guide wire.
Another problem faced by conventional guide wires involves supporting the catheter once the correct position is reached. Typically, after the guide wire is positioned, an exchange is made whereby the relatively flexible shaft is replaced by a relatively stiff shaft with a portion of the guide wire remaining in place. Although conventionally exchanging wires is a commonplace practice, the procedure undesirably adds steps in the overall procedure, and exposes the insertion area to potential contamination.
One proposal for providing an angioplasty guide wire with a controllably variable stiffness is disclosed in U.S. Pat. No. 4,676,249 to Arenas. The guide wire includes an elongated core wire and a tubular stiffening member movable within the lumen of a flexible coiled wire body defining a distal end of the guide wire. Varying degrees of flexibility are possible at the distal end by shifting the relative positions of the core wire and/or the tubular stiffening member in the wire body. U.S. Pat. No. 4,873,983 to Winters teaches a similar device that includes a tapered core wire moveable within the distal end of an outer tube to steer the distal end of the tube through a vasculature.
In both the Arenas and Winters devices, the respective stiffening features affect only the distal ends of the guide wires. Thus, support in the intermediate section of the guide wire, for example, to assist tracking of a stent catheter, is unavailable. A further disadvantage of the above-described devices involves the lack of torsional support provided by the stiffening member to ensure full rotational transmission through the wires to effect proper steering in relatively constrained blood vessels.
Another approach, disclosed in U.S. Pat. No. 5,542,434 to Imran, involves a guide wire having a core wire and a hypotube coaxially disposed around the core wire. An actuator wire formed of a memory material runs longitudinally with the core wire at the distal end of the guide wire to stiffen in response to thermal energy supplied by a heater. The core wire and hypotube are bonded together by an adhesive to prevent relative axial or torsional displacement.
While the Imran device provides a relatively stiff guide wire for purposes of torque control, such stiffness at the proximal and intermediate sections of the guide wire is permanent, and not selectively controllable. Thus, like the Arenas and Winters devices described above, the variable stiffening feature is limited to the distal end of the guide wire. Moreover, the stiffness is controllable only through use of a relatively complex and costly thermal mechanism requiring additional wires running the length of the guide wire.
Therefore, the need exists for an angioplasty guide wire having controllable elements that cooperate to provide a variable stiffness in the intermediate section of the guide wire. Moreover, the need also exists for such a guide wire having a selective locking mechanism to provide enhanced torsional control during insertion of the catheter through a vasculature. The guide wire of the present invention satisfies these needs.